Batteries produce energy from electrochemical reactions. Batteries typically include a positive electrode and a negative electrode; an ionic electrolyte solution that supports the movement of ions back and forth between the two electrodes; and a porous separator that ensures the two electrodes do not touch but allows ions to travel back and forth between the electrodes.
Contemporary portable electronic appliances rely almost exclusively on rechargeable lithium (Li)-ion batteries as the source of power. This has spurred a continuing effort to increase their energy storage capability, power capabilities, cycle life and safety characteristics, and decrease their cost. Lithium-ion battery or lithium ion cell refers to a rechargeable battery having a negative electrode capable of storing a substantial amount of lithium at a lithium chemical potential above that of lithium metal. When a lithium-ion battery is charged, lithium ions travel from the positive electrode to the negative electrode. On discharge, these ions return to the positive electrode releasing energy in the process.
In a typical Li-ion battery, the cell includes metal oxides for the positive electrode (or cathode), carbon/graphite for the negative electrode (or anode), and a lithium salt in an organic solvent for the electrolyte. More recently, lithium metal phosphates have been used as a cathode electroactive material. Lithium iron phosphate is now recognized as a safe and reliable cathode material for secondary batteries. It is a next-generation replacement for the more hazardous lithium cobalt oxide that is currently used in commercial lithium ion batteries.
These Li-ion batteries using lithium iron phosphate (LFP)-based cathode materials are currently found in cordless hand tools and on-board UPS devices. Battery packs have recently been demonstrated for transportation including aviation and rechargeable electric vehicle (REV), plug-in hybrid electric vehicle (PHEV) automobiles and buses.
New battery applications demand continuous improvements in battery discharge rate capabilities and a parallel decrease in charge times.